4,617 research outputs found
Two-way multi-lane traffic model for pedestrians in corridors
We extend the Aw-Rascle macroscopic model of car traffic into a two-way
multi-lane model of pedestrian traffic. Within this model, we propose a
technique for the handling of the congestion constraint, i.e. the fact that the
pedestrian density cannot exceed a maximal density corresponding to contact
between pedestrians. In a first step, we propose a singularly perturbed
pressure relation which models the fact that the pedestrian velocity is
considerably reduced, if not blocked, at congestion. In a second step, we carry
over the singular limit into the model and show that abrupt transitions between
compressible flow (in the uncongested regions) to incompressible flow (in
congested regions) occur. We also investigate the hyperbolicity of the two-way
models and show that they can lose their hyperbolicity in some cases. We study
a diffusive correction of these models and discuss the characteristic time and
length scales of the instability
Online real-time crowd behavior detection in video sequences
Automatically detecting events in crowded scenes is a challenging task in Computer Vision. A number of offline approaches have been proposed for solving the problem of crowd behavior detection, however the offline assumption limits their application in real-world video surveillance systems. In this paper, we propose an online and real-time method for detecting events in crowded video sequences. The proposed approach is based on the combination of visual feature extraction and image segmentation and it works without the need of a training phase. A quantitative experimental evaluation has been carried out on multiple publicly available video sequences, containing data from various crowd scenarios and different types of events, to demonstrate the effectiveness of the approach
Self-organized hydrodynamics with density-dependent velocity
Acknowledgments. This work has been supported by the Agence Nationale pour la Recherche (ANR) under grant âMOTIMOâ (ANR-11-MONU-009-01), by the Engineering and Physical Sciences Research Council (EPSRC) under grant ref. EP/M006883/1, and by the National Science Foundation (NSF) under grant RNMS 11-07444 (KI-Net). P. D. is on leave from CNRS, Institut de Math Ìematiques, Toulouse, France. He acknowledges support from the Royal Society and the Wolfson foundation through a Royal Society Wolfson Research Merit Award. H. Y. wishes to acknowledge the hospitality of the Department of Mathematics, Imperial College London, where this research was conducted. P. D. and H. Y. wish to thank F. Plourabou Ìe (IMFT, Toulouse, France) for enlighting discussions.Peer reviewedPublisher PD
Non-local first-order modelling of crowd dynamics: a multidimensional framework with applications
In this work a physical modelling framework is presented, describing the
intelligent, non-local, and anisotropic behaviour of pedestrians. Its
phenomenological basics and constitutive elements are detailed, and a
qualitative analysis is provided. Within this common framework, two first-order
mathematical models, along with related numerical solution techniques, are
derived. The models are oriented to specific real world applications: a
one-dimensional model of crowd-structure interaction in footbridges and a
two-dimensional model of pedestrian flow in an underground station with several
obstacles and exits. The noticeable heterogeneity of the applications
demonstrates the significance of the physical framework and its versatility in
addressing different engineering problems. The results of the simulations point
out the key role played by the physiological and psychological features of
human perception on the overall crowd dynamics.Comment: 26 pages, 17 figure
Long-range forces in controlled systems
This thesis investigates new phenomena due to long-range forces and their effects
on different multi-DOFs systems. In particular the systems considered are metamaterials,
i.e. materials with long-range connections. The long-range connections
characterizing metamaterials are part of the more general framework of non-local
elasticity.
In the theory of non-local elasticity, the connections between non-adjacent particles
can assume different configurations, namely one-to-all, all-to-all, all-to-all-limited,
random-sparse and all-to-all-twin. In this study three aspects of the long-range
interactions are investigated, and two models of non-local elasticity are considered:
all-to-all and random-sparse.
The first topic considers an all-to-all connections topology and formalizes the mathematical
models to study wave propagation in long-range 1D metamaterials. Closed
forms of the dispersion equation are disclosed, and a propagation map synthesizes
the properties of these materials which unveil wave-stopping, negative group velocity,
instability and non-local effects. This investigation defines how long-range
interactions in elastic metamaterials can produce a variety of new effects in wave
propagation.
The second one considers an all-to-all connections topology and aims to define an
optimal design of the long-range actions in terms of spatial and intensity distribution
to obtain a passive control of the propagation behavior which may produces
exotic effects. A phenomenon of frequency filtering in a confined region of a 1D
metamaterial is obtained and the optimization process guarantees this is the best
obtainable result for a specific set of control parameters.
The third one considers a random-sparse connections topology and provides a new
definition of long-range force, based on the concept of small-world network. The
small-world model, born in the field of social networks, is suitably applied to a
regular lattice by the introduction of additional, randomly selected, elastic connections
between different points. These connections modify the waves propagation
within the structure and the system exhibits a much higher propagation speed and
synchronization. This result is one of the remarkable characteristics of the defined
long-range connections topology that can be applied to metamaterials as well as
other multi-DOFs systems. Qualitative experimental results are presented, and a
preliminary set-up is illustrated.
To summarize, this thesis highlights non-local elastic structures which display unusual
propagation behaviors; moreover, it proposes a control approach that produces
a frequency filtering material and shows the fast propagation of energy within a
random-sparse connected material
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